1. Field
Embodiments of the present invention relate to a magnetic recording medium, a magnetic recording apparatus, and a servo control method, which use a bit-patterned medium.
2. Description of the Related Art
Technology called a “pre-servo” method of forming servo patterns on a bit-patterned medium simultaneously with the formation of bit patterns thereon, based on the intensity of magnetization thereof and the volumes of magnetic materials provided thereon, and then performing servo-writing by the single-directional magnetization of the entire surface of the medium is a major candidate for technology applied to the process of forming a servo pattern. Hitherto, servo patterns configuring servo frames provided on the medium, e.g., patterns called servo preambles and servo addresses provided thereon extend continuously from the outer edge to the inner edge of the medium. If a magnetic film (e.g., CoCr—SiO2-based granular film) to be subjected to conventional vertical magnetic recording is used, the magnetization state thereof is stable after the servo-writing. However, if a magnetic film (e.g., FePt or CoPt based single-magnetic-domain film) specialized to a bit-patterned medium is used, unintended magnetic walls are formed on servo patterns due to external energy such as thermal disturbance. That is, although all servo patterns formed in servo frames should be magnetized in a single direction (e.g., N-direction), the magnetization direction of the servo frames is naturally changed to the opposite direction (e.g., S-direction) due to the occurrence of magnetic walls. This causes noise and address-decoding-error. Effective countermeasures against this phenomenon are to reduce the areas of the patterns in the servo frames and to segmentalize each of the patterns. However, from the viewpoint of servo control, to detect a radial position continuously, it is necessary that information recorded on each servo frame is normally reproduced at any radial position.
Accordingly, it is devised that the patterns are provided at positions which are radially discrete and circumferentially different from one another. However, no means is known, which uses the configuration of the entire servo patterns and implements better reproduction.